This invention relates to compositions and methods useful for contraception and for treatment of benign gynecological disorders in mammals, especially human females. More particularly, the present invention is directed to contraceptive methods and methods of treating benign gynecological disorders and preparations for use therein which are effective for reducing exposure to progestational agents.
The first progestogen antagonist synthesized and tested was RU 486[RU 38486; 17-hydroxy-11-(4-dimethylaminophenyl)-17-(prop-1-ynyl)estra -4,9-dien-3-one; beta-[(4-N,N-dimethylamino)-phenyl]-17.beta.-hydroxy- 17.alpha.-propynyl-4,9(10)-oestradiene-3-one; mefepristone]. Mifepristone has high affinity for the progesterone receptor, with predominantly antiprogestational effects. Mifepristone is known to have growth-inhibitory effects in breast cancer cells in in vitro and in vivo preclinical studies and in human clinical trials [Klijn, J. G. M. et al., Cancer Research 49:2851-2856 (1989)]. Other antiprogestational agents have been synthesized and tested including ZK 98.299 (onapristone) and ZK 112.993, which also have antitumor efficacy [Michna, H. et al., J. Steroid Biochem. Molec. Biol. 43:203-210 (1992)].
Mifepristone is known to be useful as a medical abortifacient (because of its antiprogestational activities) and as a postcoital contraceptive. Mifepristone has been evaluated as a potential contraceptive agent using several schedules. A single dose of mefepristone late in the menstrual cycle may be a useful contraceptive approach [Nieman, L. K. et al., N. Engl. J. Med. 316:187-191 (1987)].
Protracted (i.e., 3 month) administration of 100 mg per day mefepristone alone to premenopausal women has been shown to inhibit ovulation and ovarian progesterone production, while maintaining early follicular phase levels of estradiol, estrone and testosterone [Kettel, L. M. et al., Fertil. Steril. 56:402-407 (1991)]. These effects may be mediated through a progesterone agonist effect of mefepristone on the hypothalamic-pituitary unit, although other mechanisms are possible.
Several new regimens of progesterone antagonists and progestins have been described. One such regimen [Kekkonen, R. et al, Fertil. Steril. 53:747-750 (1990)] consists of 25 mg of mefepristone on days 1 to 14 of a 28-day treatment cycle followed by norethisterone on days 15 to 24 of the cycle. A subsequent report describes a regimen consisting of 25 mg of mefepristone on days 1 to 21 of a 31-day treatment cycle followed by norethisterone 5 mg per day or medroxyprogesterone acetate 5 mg per day taken on days 22 to 31 [Kekkonen, R. et al., Fertil. Steril. 60:610-615 (1993)].
These administration sequences are designed to mimic the physiological secretion of steroids in the menstrual cycle, with a progestational steroid administered over a 10 day period following 14 to 21 days of administration of the progestogen antagonist. With such a regimen, approximately 30% of days are associated with exposure to the progestogen.
PCT Patent Applications WO 93/21926 and 93/21927 to Hodgen (the entire disclosures of which are hereby incorporated by reference) describes the protracted administration of a progestogen, with administration of an antiprogestational compound on the 28th or 30th day of the treatment cycle. The contraceptive compositions described by Hodgen provides for an even greater number of days of exposure to the progestogen component than in the normal menstrual cycle.
The breast has a tightly regulated pattern of growth primarily under the control of steroid hormones. The effects of steroid hormones on the normal breast are increasingly well understood. Estrogen induces some breast epithelial proliferation, but estrogen and progesterone together produce even greater cell proliferation [Pike, M.C. et al., Epidemiol. Rev. 15:17-35 (1993)]. In non-pregnant premenopausal women the breast epithelium undergoes repetitive periods of cell proliferation and cell loss secondary to cyclic ovarian activity. In the terminal duct lobular unit (TDLU) of the premenopausal breast, cell proliferation is low during the follicular phase of the menstrual cycle. Following ovulation, progesterone is produced by the corpus luteum and TDLU cell proliferation increases two- to three-fold over follicular levels [Pike et al. (1993), supra]. Consistent with the breast cell proliferation rates, the size and number of terminal ductules peak during the late-luteal phase [Longacre, T. A. & Barlow, S. A., Am. J. Surg. Path. 10:382-393 (1986)]. If fertilization and pregnancy do not ensue, progesterone levels fall, the rate of breast cell division decreases, and a wave of cell death by apoptosis follows the peak in cell proliferation [Anderson, T. J. et al., Br. J. Cancer 46:376-382 (1982)].
Proliferating cell populations are more susceptible to carcinogenic effects, and the rise in cancer risk associated with cell proliferation is secondary to an increased chance of mutation and loss of tumor suppressor genes [Preston-Martin, S. et al., Cancer Res. 50:7415-7421 (1990)]. Thus, breast cancer risk would be predicted to increase the greatest during periods of exposure to both estrogen and progestogen, as in the premenopausal period or in women receiving combined oral contraceptives (COCs); less during periods of exposure only to estrogen, as in postmenopausal women receiving estrogen replacement therapy (ERT) or in obese postmenopausal women; and least during periods of exposure to very low levels of both hormones, as in non-obese postmenopausal Asian women.
The heretofore-identified regimens comprising administration of an antiprogestational agent in sequence with a progestogen are thus not entirely satisfactory. In particular, they result in exposure to progestogens for a period of time similar to a normal menstrual cycle, and to a similar or greater amount of progestational action. As such, they may result in a breast cancer risk similar to or possibly greater than that of a normal ovulating woman.
U.S. Pat. No. 5,211,952 to Spicer et al. (the entire disclosure of which is also hereby incorporated by reference) describes administration of a progestational agent every two months to six months, with administration of a gonadotropin hormone releasing hormone and an estrogen.
It is an object of the present invention to provide regimens for contraception and the treatment of benign gynecological disorders which would obviate the problems attendant to the use of existing methods of birth control and treatment regimens.
In particular, it is an object of the present invention to reduce the risk of adverse consequences associated with the heretofore known methods.